Yes, I can tell when people are gay. It's the way they walk and their mannerism. They'll use certain phrase like,"My partner and I went to the store" instead of boyfriend. One can judge them from their facebook if they like anything gay related only gay people would understand.

Having said that, there are certainly things you can do to "hone" your gaydar. But at the end of the day it's a matter of any aptitude and you either have to have the foundational aptitude or you'll never get to real proficiency. Like a virtuoso pianist has to be born with the aptitude THEN have years of practice to achieve the true proficiency versus a good piano player who isn't a virtuoso, didn't have the aptitude but worked HARD to attain the skills and can play decently but not with awe-inspiring results. Such is gaydar..... in our opinion.